This invention relates to a high output semiconductor laser having a single lobe output beam and an optical output of 100 mW or more.
As a candidate for a realizable semiconductor laser of 100 mW or more optical output, there is available a so-called phased array type semiconductor laser having a plurality of luminous stripes which may be brought into mutual optical coupling. In this type of semiconductor laser, however, a higher order supermode tends to oscillate and hence the output beam becomes a two-lobe beam, resulting in inconveniences to practical applications.
The concept of the supermode is described in Optics Letters, page 125, April, 1984. The reason why the higher order supermode is selected in the aforementioned type of semiconductor laser will be explained with reference to FIG. 1. In the conventional phased array type laser, refractive index is related to gain (or loss) as graphically illustrated in FIG. 1. It will be seen from FIG. 1 that the gain is predominant in regions of larger refractive index while a large loss is predominant in regions of smaller refractive index. There are also depicted in FIG. 1 an electric field distribution for a fundamental supermode and an electric field distribution for a higher order supermode under the above conditions. In the regions of the large loss, the amplitude of the fundamental supermode is not null while the amplitude of the higher order supermode is null. Namely, optical loss of the higher order supermode is smaller than that of the fundamental supermode and consequently, the higher order supermode is subject to a lower threshold gain than the fundamental supermode. For the above reason, the higher order supermode oscillates in the conventional laser to produce a two-lobe output beam.